Regents Chemistry Exam Explanations January 2011

Base your answers to questions 66 through 68 on the information below.

In the early 1800s, John Dalton proposed an atomic theory that was based on experimental observations made by several scientists. Three concepts of Dalton’s atomic theory are stated below.

Statement A: Atoms are indivisible and cannot be destroyed or broken down into smaller parts.

Statement B: Atoms of one element cannot be changed into atoms of another element.

Statement C: All atoms of one element have the same mass.

66 Explain, in terms of particles, why statement A is no longer accepted. [1]

HIGHLIGHT TO SEE THE ANSWER

Smaller parts of atoms exist, such as protons, neutrons, and electrons.

During some nuclear reactions, unstable atoms can spontaneously decay into smaller particles.

Atoms can lose electrons.

67 The decay of N-16 is represented by the balanced equation below.

State evidence that indicates statement B is not always true. [1]

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An atom of nitrogen (atomic number 7) changed into an atom of oxygen (atomic number 8).

The decay of N-16 atoms produced O-16 atoms.

Radioactive decay results in an element being changed into another element.

68 Explain, in terms of particles in the atoms of an element, why statement C is false. [1]

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Atoms of different isotopes of an element have different masses because they have different numbers of neutrons.

Atoms of an element can differ in the number of neutrons and, therefore, masses.

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